Abstract
We theoretically investigate a multi-resonant plasmonic metamaterial perfect absorber operating between 600 and 950 nm wavelengths. The presented device generates 100% absorption at two resonance wavelengths and delivers an ultra-narrow band (sub-20 nm) and high quality factor resonance. The studied perfect absorber is a metal–insulator–metal configuration where a thin MgF spacer is sandwiched between an optically thick gold layer and uniformly patterned gold circular nanodisc antennas. The localized and propagating nature of the plasmonic resonances are characterized and confirmed theoretically. The origin of the perfect absorption is investigated using the impedance matching and critical coupling phenomenon. We calculate the effective impedance of the perfect absorber and confirm the matching with the free space impedance. We also investigate the scattering properties of the top antenna layer and confirm the minimized reflection at resonance wavelengths by calculating the absorption and scattering cross sections. The excitation of plasmonic resonances boost the near-field intensity by three orders of magnitude which enhances the interaction between the metamaterial surface and the incident energy. The refractive index sensitivity of the perfect absorber could go as high as nm/RIU. The presented optical characteristics make the proposed narrow-band multi-resonant perfect absorber a favorable platform for biosensing and contrast agent based bioimaging.
Highlights
Plasmonic metamaterial perfect absorbers (PA) [1,2,3,4,5,6] have attracted tremendous attention as they can fully absorb the incident light at optical frequencies [7,8,9,10,11,12] and allow a variety of exotic applications [13,14,15,16,17]
PAs can be typically designed using three functional layers that comprise a dielectric interlayer sandwiched between the bottom metal film and a patterned top metal plasmonic nanoantenna serving as a resonator [18,19,20,21,22]
We present a multi-resonant plasmonic metamaterial perfect absorber operating in the NIR region
Summary
Plasmonic metamaterial perfect absorbers (PA) [1,2,3,4,5,6] have attracted tremendous attention as they can fully absorb the incident light at optical frequencies [7,8,9,10,11,12] and allow a variety of exotic applications [13,14,15,16,17]. A nanoantenna which exhibits only an electric dipole response is most absorptive if the absorbed power is identical to its scattered power This condition is known as critical coupling [35,36,37,38] and appears when the radiative and intrinsic (non-radiative) damping rates, γr and γi , respectively, of the designed system becomes identical to each other via precise selection of the dielectric spacer thickness. This leads to similar absorption and scattering cross sections (Cabs ≈ Csca ), and most of the incident energy is absorbed by the system [34,39].
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